CN106495992A

CN106495992A - A kind of phenol ortho alkylation method

Info

Publication number: CN106495992A
Application number: CN201610913604.4A
Authority: CN
Inventors: 郭骄阳
Original assignee: BEIJING JIYI CHEMICALS Co Ltd
Current assignee: BEIJING JIYI CHEMICALS Co Ltd
Priority date: 2016-10-19
Filing date: 2016-10-19
Publication date: 2017-03-15

Abstract

The present invention provides a kind of phenol type substances ortho alkylation method, in the presence of a catalyst, phenol type substances and alkylation reactions；Described catalyst is that zinc and phenol compound reaction prepare the aryl zinc salt for generating, and described alkylating agent is alkene；Described phenol type substances include：The polyhydric phenols such as catechol, hydroquinones, also include one to two alkyl, or the phenols of halogen；Described alkyl is the straight or branched alkane of 1 10 carbon；The present invention substantially improves preparation efficiency, while conversion ratio is further improved, while present invention also offers preparing the method for 2,6 di-tert-butyl methyl phenols and the reactor for preparing.

Description

A kind of phenol ortho alkylation method

Technical field

The present invention relates to the alkylation of phenol, more particularly to the system of 2,6- DI-tert-butylphenol compounds (referred to as 2,6 phenol) class Standby.2,6 di t butyl phenol class is the primary raw material of hindered phenol anti-oxidants.

Background technology

Phenol includes the polyhydric phenols such as catechol, hydroquinones, also includes and there are one to two alkyl, or the phenol of halogen Class.Such as ortho-methyl phenol, p-methyl phenol, 2,4 xylenols, orthomonochlorphenol, parachlorphenol, 2,4 dichloride base phenol.Alkyl also may be used To be methyl, ethyl, propyl group, butyl, the straight or branched alkane of 1-10 carbon.

The alkylated reaction for obtaining 2,6 phenols can realize using kinds of processes route that 2,6 phenol of early stage production are mostly with three Al 2 O is catalyst, at high temperature under high pressure synthesis 2,6- DI-tert-butylphenol compounds.Its advantage is that catalyst is cheap and easy to get, catalysis Life-span length, can both adopt intermittent reaction thermopnore pattern, it would however also be possible to employ successive reaction fixed bed mode, have the disadvantage：Reaction turns Rate is low, usually 20-30%, poor selectivity, and generally in 10-15%, equipment volume is huge, and energy ezpenditure is higher.

The phenol that the patent application of Application No. CN200910065459.5 discloses a kind of high conversion high selectivity is adjacent Position alkylation, which adopts aryl aluminium salt as catalyst.However, on the one hand its transformation efficiency still needs to be carried with selective Height, on the other hand, aluminium needs the extra care in operation due to having toxicity to human body.Additionally, preparing 2,6-, bis- tertiary fourths During base phenol, there is the defects such as unstable properties, service life be short in traditional reactor.Therefore urgently there is new benzene this area The preparation method of aldehydes matter ortho alkylation method, especially 2,6 di t butyl phenol occurs.

Content of the invention

On the one hand, the present invention proposes a kind of phenol type substances ortho alkylation method, it is characterised in that deposit in catalyst Under, phenol type substances and alkylation reactions, to generate alkylating phenol type substances, such as 2,6- DI-tert-butylphenol compounds.

In methods described, the catalyst for being used is that zinc and phenol compound reaction prepare the aryl zinc salt for generating, institute The alkylating agent that states be alkene, such as isobutene；

Described phenol type substances include the polyhydric phenols such as catechol, hydroquinones, and have one to two alkyl or The phenols of halogen, wherein described alkyl are the straight or branched alkane of 1-10 carbon atom；The phenol type substances are for example right Methylphenol；

At the beginning of reaction, zinc puts into alkylated reaction with weight than 1.0-6.0% with phenol type substances；

After reaction terminates, by following steps Removal of catalyst：Unnecessary isobutene desorption is reclaimed, into reaction vessel The water of injection zinc weight 2-20 times, stirs to destroy catalyst at 50-90 DEG C, and mixing time is 10-25 minutes, using filtration Zinc hydroxide is removed by mode, unnecessary water distillation condensation reclaim after reuse capable of circulation, rectifying column be fractionated with neighbour Light fraction based on phenol can return alkylated reaction use.

The reaction vessel can be reactor, reactor preferably provided by the present invention.

The zinc for being used is preferably fresh spherical shape zinc, and, preferably in the scope of 1-100mm, storage time is preferably little for its diameter In 60 days.

On the other hand, the present invention proposes a kind of method for preparing BHT, and which adopts aryl Zinc salt is catalyst, and concrete steps include that zinc ball and p-methyl phenol is reacted in a kettle. at moderate temperatures makes aryl Zinc salt catalyst, is cooled to about 70 DEG C, discharges hydrogen, into reactor imports isobutene, under the conditions of 90-110 DEG C, reacts 2- 3 hours, obtain BHT.Application the method, can obtain 96.8% conversion ratio.；

Another further aspect, the present invention provide one kind and are suitable to prepare alkylating phenol type substances, preferably 2,6- di-t-butyls pair The reactor of methylphenol, which carries magnetic drive, including kettle (1), the motor (9) being arranged on above outside kettle, electricity Outer steel assembly (8) and interior magnet steel assembly (6) is provided with below machine (9), between outer steel assembly (8) and interior magnet steel assembly (6) Cage (7) is provided with, outer steel assembly (8) is provided with the mounting flange (5) being fixedly connected, motor with kettle (1) junction (1) output end is connected with and extends to the internal power transmission shaft (4) of kettle (1), is provided with shaft coupling (3), joins in axle below power transmission shaft Device (3) end is provided with agitator (8).

In one embodiment, the reactor outer surface is coated with corrosion-resistant coating.

In one embodiment, the corrosion-resistant coating includes bond coating and anti-oxidant superficial layer.

Wherein, the bond coating through the following steps that prepare：Using molybdenum 6-8 parts, nickel 4-6 parts, silicon 7-9 parts, zirconium 0.5-1.5 parts, aluminium 2-4 parts, silica 0.5-1.5 parts, boron oxide 1-3 parts, titanium oxide 0.5-1.5 parts, aluminum oxide 0.5-1.5 Part, chromium 1-3 parts, the alloy powder of tungsten 1-3 parts are sprayed at reactor surfaces externally and internally with plasma spraying machine, and coating layer thickness is 0.1-0.2mm.

Preferably, the bond coating through the following steps that prepare：Using 7 parts of molybdenum, 5 parts of nickel, 8 parts of silicon, 1 part of zirconium, 3 parts of aluminium, silica 1 part, 2 parts of boron oxide, 1 part of titanium oxide, 1 part of aluminum oxide, 2 parts of chromium, the alloy powder that 2 parts of tungsten, with etc. from Sub- flush coater is sprayed at reactor surfaces externally and internally, and coating layer thickness is for about 0.15mm.

The anti-oxidant surface layer through the following steps that prepare：Using molybdenum 0.5-1.5 parts, silicon 2-4 parts, zirconium 4-6 parts, nickel 0.5-1.5 parts, aluminium 1-3 parts, carbon 0.02-0.04 parts, phosphorus 0.01-0.03 parts, cobalt 0.5-1.5 parts, silica 4-6 parts, oxidation Aluminium 0.5-1.5 parts, yttrium 2-4 parts, tungsten 1-3 parts, vanadium 1-3 parts, the alloy powder of lanthanum 0.5-1.5 parts are sprayed with plasma spraying machine In reactor surfaces externally and internally, coating layer thickness is 0.1-0.3mm.

Preferably, the anti-oxidant surface layer through the following steps that prepare：Using 1 part of molybdenum, 3 parts of silicon, 5 parts of zirconium, nickel 1 Part, 2 parts of aluminium, 0.03 part of carbon, 0.02 part of phosphorus, 1 part of cobalt, 5 parts of silica, 1 part of aluminum oxide, 3 parts of yttrium, 2 parts of tungsten, 2 parts of vanadium, lanthanum 1 The alloy powder of part, is sprayed at reactor surfaces externally and internally with plasma spraying machine, and coating layer thickness is for about 0.2mm.

The phenol type substances ortho alkylation method of the present invention and the method for preparing 2,6- di-tert-butyl methyl phenols The aryl zinc salt for generating is prepared as catalyst using zinc and phenol compound reaction, reaction speed is accelerated, is substantially improved Preparation efficiency, while further increasing conversion ratio, the conversion ratio of BHT can reach 96.8%. Additionally, due to the stainless steel cauldron employed with magnetic drive, which drives agitator by magnetic drive, increased Stirring efficiency, the corrosion-resistant coating of the kettle trypsin method of reactor greatly strengthen corrosion resistance, under various complex environments all Can steady operation, and service life greatly increases, practice have shown that, it is possible to use at least more than 45 years.

Description of the drawings

Fig. 1 is the structural representation of the stainless steel cauldron with magnetic drive according to the embodiment of the invention Figure.

Fig. 2 is profiles of the Fig. 1 along A-A directions.

Wherein reference is respectively：1. motor；2. agitator；3. shaft coupling；4. power transmission shaft；5. mounting flange；6. in Magnet steel assembly；7. cage；8. outer steel assembly；9. motor.

Specific embodiment

Catalyst in the application is that zinc and phenol or the reaction of the phenol compound containing other functional groups are prepared and generated Aryl zinc salt.

Its general structure is：

In formula, R can be linear paraffin, branched paraffin or the halogen of H or 1-10 carbon atom.

, with methylic phenol (calling methylphenol in the following text) ortho alkylation method and 2,6 phenol are concrete as a example by preparing for the application The present invention is described, its preparation process is comprised the following steps substantially：

1. the preparation of catalyst triple phenoxyl zinc：

Raw material zinc is provided, which can adopt commercially available zinc, and preferred ball zinc of the diameter in 1-100mm scopes, just to process Good zinc is optimal, storage time preferably smaller than 60 days；

Raw material zinc is 1.0-6.0%, preferably 2.0%-4.0% with the weight ratio of methylphenol；

Spherical zinc and methylphenol are put into reaction vessel (reaction for example provided by the present invention with above-mentioned mass ratio Kettle) in, stirring and be suitable at such as 100-180 DEG C of the temperature of reaction, zinc enters line replacement reaction with methylphenol, releases hydrogen Gas.Now there is pressure to produce in container, generally in 0.1-0.4Mpa (gauge pressure).Kept for reaction 20-25 minutes, kettle temperature is down to 70 Below DEG C, hydrogen in kettle is discharged, obtain zinc catalyst.

Zinc catalyst can be prepared in closed autoclave, it is also possible to prepared in atmospheric kettle.

2. alkylated reaction：

Alkylating agent (is illustrated by taking isobutene as an example), is passed through in for example little autoclave of reaction vessel.Reaction temperature 90-110 DEG C is set to, preferably 95-105 DEG C.Isobutene is 2-3.0: 1, preferably 2.3: 1 with the molar ratio of methylphenol；Instead Pressure is answered to be set to 0-2.0Mpa, preferably 0.2-1.2mpa.

With the carrying out of alkylated reaction, in kettle, isobutene gas pressure is gradually reduced, after pressure is down to about 0.4Mpa, The reactant liquor constantly extracted in kettle is detected, when reaction reaches predetermined value, you can cooling terminating reaction.

Alkylated reaction can be carried out under pressurization, normal pressure or reduced pressure.

3. the removing of catalyst：

After unnecessary isobutene desorption in kettle is reclaimed, use for lower secondary response.

Water is injected into reactor, the weight of water is 2-20 times of the weight of zinc, by zinc catalyst under 50-90 DEG C of stirring Destruction.Preferred amount of water is 10-15 times of zinc, stirs 10-25 minutes preferably at temperature 60-80 DEG C.

Using filter type by Zn (OH)₂Remove.Reuse capable of circulation after unnecessary water distillation condensation recovery.So as to keep away Phenol wastewater discharge is exempted from.

Limpid reactant liquor after filtration enters rectification and purification operation.The light fraction based on adjacent phenol being fractionated first is made Use for alkylated reaction for aldehydes matter.Continue rectifying, as a example by preparing with 2,6- DI-tert-butylphenol compounds, tower top obtains purity and is More than 99.6% methylphenol alkylate.

Examples below 2-6 reactors as shown in Figure 1-2 used, which carries the stainless steel of magnetic drive, including kettle Body 1, the motor 9 for being arranged on top outside kettle, are provided with outer steel assembly 8 and interior magnet steel assembly 6, outer steel below motor 9 It is provided with cage 7 between assembly 8 and interior magnet steel assembly 6, outer steel assembly 8 is provided with 1 junction of kettle and is fixedly connected Mounting flange 5,1 output end of motor are connected with the power transmission shaft 4 extended to inside kettle 1, are provided with shaft coupling 3 below power transmission shaft, 3 end of shaft coupling is provided with agitator 8, reactor surfaces externally and internally is coated with corrosion-resistant coating.

Corrosion-resistant coating includes bond coating and anti-oxidant superficial layer.Bond coating is prepared by following steps：Using molybdenum 7 Part, 5 parts of nickel, 8 parts of silicon, 1 part of zirconium, 3 parts of aluminium, silica 1 part, 2 parts of boron oxide, 1 part of titanium oxide, 1 part of aluminum oxide, 2 parts of chromium, tungsten 2 parts of alloy powder, is sprayed at reactor surfaces externally and internally with plasma spraying machine, and coating layer thickness is 0.15mm.Anti-oxidant surface layer Prepared by following steps：Using 1 part of molybdenum, 3 parts of silicon, 5 parts of zirconium, 1 part of nickel, 2 parts of aluminium, 0.03 part of carbon, 0.02 part of phosphorus, 1 part of cobalt, two 5 parts of silica, 1 part of aluminum oxide, 3 parts of yttrium, 2 parts of tungsten, 2 parts of vanadium, the alloy powder that 1 part of lanthanum are sprayed at instead with plasma spraying machine Kettle surfaces externally and internally is answered, coating layer thickness is 0.2mm.

Embodiment 1

1500 grams of 2,4- xylenols and 100 grams of zinc balls are weighed, is placed in 10 liters of round-bottomed flasks, heating makes zinc and diformazan Base phenol reactant, discharges hydrogen.After the reaction thoroughly of zinc ball.70 DEG C are cooled the temperature to, into flask, is passed through isobutene, with The carrying out of reaction, in bottle, the volume of material is continuously increased, and when volume increases to 5-8 times, sample analysis are as a result as follows：

2,4- dimethyl 6- tert-butyl phenols	96.1%
		2,4- xylenols	2.4%
Remaining alkyl phenol	1.5%

Above-mentioned reaction result 2, the selectivity of 4- dimethyl 6- tert-butyl phenols be 96.1%, and 2,4- xylenols turn Rate is 97.6%.

Embodiment 2

About 30 grams of spherical zinc for processing are put into into 5 liters of little autoclaves, about 1175 grams of phenol are added, and are heated up Hydrogen is released in 110 DEG C of reactions, keeps reaction 25 minutes.70 DEG C are cooled the temperature to, and after discharge hydrogen, about 1610 grams are imported into kettle Isobutene.Reaction temperature is controlled at 90-110 DEG C.Now in kettle pressure in 1.0-1.2Mpa.

With the carrying out of reaction, in kettle, pressure is gradually reduced, and when pressure is down to 0.3Mpa, samples and examines through gas chromatograph Survey, reactant liquor composition is as follows：

Phenol	Adjacent phenol	2,6 phenol	2,4 phenol	2,4,6 phenol	Remaining alkyl phenol
						0.2wt%	2.3wt%	89.2wt%	0.3wt%	6.5wt%	1.5wt%

The annotation of abbreviation in upper table, adjacent phenol：O-tert-butylphenol；

2,4 phenol：2,4-DTBP；

2,4,6 phenol：2,4,6- tri-butyl-phenols.

Found out by above-mentioned reaction result：Conversion ratio 99.8% in terms of phenol, 2,6 phenol selective 89.2%.Unnecessary isobutyl Alkene is reclaimed through compressor and is used for lower secondary response.160 grams of water are injected into kettle, stir 15 minutes, by catalyst three at 90 DEG C Phenoxy group zinc is hydrolyzed into zinc hydroxide and phenol, and reactant liquor is poured in the filter tunnel equipped with accurate filter paper, filters zinc hydroxide Obtain limpid alkylated reaction liquid afterwards and send to rectifying, the condensed recovery of unnecessary water returns, for hydrolysis destruction next time catalyst Use.The light fraction using adjacent phenol based on that rectifying tower top is fractionated can be used as aldehydes matter for alkylated reaction.

Embodiment 3

1500 grams of p-methyl phenol, 50 grams of zinc ball is weighed, is placed in little autoclave, Heating Zn ball and p-methyl phenol are anti- Should, it is successfully prepared catalyst.70 DEG C are cooled to, hydrogen is discharged, and the isobutene of 3500ml is imported into kettle.In 95-105 DEG C of condition Under, 2-3 hours are reacted, sample analysis are as a result as follows：

2,6- bis- tertiary fourth p-methyl phenols	95.1%
		Orthoresol	3.9%
Paracresol	1.0%

The present embodiment 2, the selectivity 95.1% of bis- tertiary fourth p-methyl phenols of 6-, paracresol reaction conversion ratio 99.0%.

Embodiment 4

15kg ortho-methyl phenols, 600 grams of zinc balls are put in 50 liters of autoclaves.Heating ortho-methyl phenol is made with zinc reaction Catalyst, lowers the temperature 60 DEG C, after discharging hydrogen, is passed through the mixing carbon containing isobutene with the speed that 10-20 per hour rises into kettle Four components, while extracting four component of carbon for having neither part nor lot in reaction with petroleum gas compressor out, maintain -0.1- the pressure of reactor 0Mpa, insulation reaction 2-3 hour at 70-90 DEG C, sample analysis reactant liquor are as a result as follows：

2- methyl 6- tert-butyl phenols	90.6%
		2- methylphenols	3.9%
Remaining alkyl phenol	5.5%

Reaction result purpose product, 2- methyl 6- tert-butyl phenols selectively reach 90.6%, aldehydes matter conversion ratio 96.1%.

Embodiment 5

2500kg phenol, 50kg zinc balls is put into into 10000 liters of reactors.Under the conditions of 160 DEG C, phenol is reacted with zinc ball Make zinc catalyst.Kettle temperature is down to 70 DEG C, hydrogen is discharged, and 5750 liters of isobutenes is imported into kettle, under the conditions of 95-105 DEG C Reaction 12-16 hours, terminate reaction sample analysis, 2,6 phenol selective 88.6%, phenol conversion 99.74%.As a result as follows：

Phenol	Adjacent phenol	2,6 phenol	2,4 phenol	2,4,6 phenol	Remaining alkyl phenol
						0.45%	2.2%	86.6%	0.3%	8.0%	2.0%

Unnecessary isobutene parsing in kettle is reclaimed after terminating and is used for lower secondary response by reaction.Into kettle, injection rectifying is reclaimed Phenol wastewater 200kg, at 80 DEG C stir 30 minutes, zinc hydroxide is filtered by oil filter, the limpid reaction after filtration Liquid send rectifying column purification to respectively obtain water containing phenol, the light fraction based on adjacent phenol, 2,6 phenol of purpose product and with 2, and 4,6 phenol are Main heavy distillat.

Embodiment 6

400kg phenol, 7.6kg zinc balls is put into into 2000 liters of autoclaves, and intensification makes phenol and zinc reaction make catalyst, The hydrogen of generation is discharged.Rectifying column reclaims the light fraction based on adjacent phenol, and predominant amount is as follows：

Phenol	Adjacent phenol	2,6 phenol	Remaining alkyl phenol
				10%	60%	5%	25%

The light fraction 200kg of above-mentioned composition is put in the successful reactor of catalyst preparation.1120 are passed through into kettle The isobutene mixture of fresh and recovery being risen, 2-3 hours being reacted at 90-110 DEG C, sample analysis result is as follows：

Phenol	Adjacent phenol	2,6 phenol	2,4 phenol	2,4,6 phenol	Remaining alkyl phenol
						0.30%	1.78%	86.6%	0.32%	8.2%	2.80%

2,6 phenol of this example purpose product selective 86.6%, phenol conversion 99.7%.

Claims

1. a kind of phenol type substances ortho alkylation method, it is characterised in that in the presence of a catalyst, phenol type substances and alkyl Agent is reacted, to generate alkylating phenol type substances；

Wherein, described catalyst is that zinc and phenol compound reaction prepare the aryl zinc salt for generating, described alkyl Agent is alkene, for example isobutene；

Described phenol type substances include catechol, the polyhydric phenols such as hydroquinones, and also including with one to two alkyl Or the phenols of halogen, described alkyl is the straight or branched alkane of 1-10 carbon atom；The phenol type substances are for example to first Base phenol；

At the beginning of reaction, zinc puts into alkylated reaction with weight ratio as 1.0-6.0% with the phenol type substances；

After alkylated reaction terminates, by following steps Removal of catalyst：Unnecessary alkene desorption is reclaimed, into reaction vessel The water of injection zinc weight 2-20 times, stirs to destroy catalyst at 50-90 DEG C, and mixing time is 10-25 minutes, using filtration Zinc hydroxide is removed by mode, unnecessary water distillation condensation reclaim after reuse capable of circulation, rectifying column be fractionated with neighbour Light fraction based on phenol can return alkylated reaction use.

2. phenol type substances ortho alkylation method according to claim 1, it is characterised in that described zinc is fresh spherical shape Zinc, its diameter should be in 1-100mm, and storage time should be less than 60 days.

3. a kind of method for preparing BHT, it is characterised in that make at moderate temperatures zinc ball with to first Base phenol reacts in a kettle. makes aryl zinc salt catalyst, is cooled to about 70 DEG C, discharges hydrogen, imports different into reactor Butylene, under the conditions of 90-110 DEG C, reacts 2-3 hours, obtains BHT.

4. a kind of reactor for preparing alkylating phenol type substances, preferred BHT, its are special Levy and be that the reactor is the stainless steel cauldron with magnetic drive, including kettle (1), be arranged on top outside kettle Motor (9), be provided with outer steel assembly (8) and interior magnet steel assembly (6), outer steel assembly (8) and interior magnet steel below motor (9) Cage (7) is provided between assembly (6), and outer steel assembly (8) is provided with the Method for Installation being fixedly connected with kettle (1) junction Blue (5), motor (1) output end are connected with and extend to the internal power transmission shaft (4) of kettle (1), are provided with shaft coupling below power transmission shaft (3) shaft coupling (3) end is provided with agitator (8),.

5. reactor according to claim 4, it is characterised in that the reactor surfaces externally and internally is coated with anticorrosive painting Layer.

6. reactor according to claim 5, it is characterised in that the corrosion-resistant coating includes bond coating and antioxygen table Surface layer；

The bond coating is through the following steps that preparation method：Using molybdenum 6-8 parts, nickel 4-6 parts, silicon 7-9 parts, zirconium 0.5- 1.5 parts, aluminium 2-4 parts, silica 0.5-1.5 parts, boron oxide 1-3 parts, titanium oxide 0.5-1.5 parts, aluminum oxide 0.5-1.5 parts, Chromium 1-3 parts, the alloy powder of tungsten 1-3 parts are sprayed at reactor surfaces externally and internally with plasma spraying machine, and coating layer thickness is 0.1- 0.2mm；

The anti-oxidant surface layer through the following steps that prepare：Using molybdenum 0.5-1.5 parts, silicon 2-4 parts, zirconium 4-6 parts, nickel 0.5- 1.5 parts, aluminium 1-3 parts, carbon 0.02-0.04 parts, phosphorus 0.01-0.03 parts, cobalt 0.5-1.5 parts, silica 4-6 parts, aluminum oxide 0.5-1.5 parts, yttrium 2-4 parts, tungsten 1-3 parts, vanadium 1-3 parts, the alloy powder of lanthanum 0.5-1.5 parts are sprayed at plasma spraying machine Reactor surfaces externally and internally, coating are thickness 0.1-0.3mm.

7. reactor according to claim 6, it is characterised in that the bond coating is through the following steps that prepare： Using 7 parts of molybdenum, 5 parts of nickel, 8 parts of silicon, 1 part of zirconium, 3 parts of aluminium, silica 1 part, 2 parts of boron oxide, 1 part of titanium oxide, 1 part of aluminum oxide, 2 parts of chromium, the alloy powder that 2 parts of tungsten are sprayed at reactor surfaces externally and internally with plasma spraying machine, and coating layer thickness is 0.15mm；

The anti-oxidant surface layer preparation method is：Using 1 part of molybdenum, 3 parts of silicon, 5 parts of zirconium, 1 part of nickel, 2 parts of aluminium, 0.03 part of carbon, phosphorus 0.02 part, 1 part of cobalt, 5 parts of silica, 1 part of aluminum oxide, 3 parts of yttrium, 2 parts of tungsten, 2 parts of vanadium, the alloy powder that 1 part of lanthanum use plasma Flush coater is sprayed at reactor surfaces externally and internally, and coating layer thickness is 0.2mm.

8. the method for preparing BHT as claimed in claim 3, it is characterised in that the reactor For the reactor described in any one of claim 4-7.